In the past, in a continuous casting facility, to cause nonmetallic inclusions included in the molten steel in a mold and bubbles of Ar gas blown into an immersion nozzle to rise to the surface of the molten steel without being trapped in the slab and thereby obtain a good quality slab, the method has been used of stirring the molten steel in the mold by electromagnetic force. Various proposals have been made in the past relating to electromagnetic stirrer coils for stirring molten steel in a mold by electromagnetic force.
For example, Japanese Patent No. 3273105 discloses a fluid motion control system providing a second core abutting against a back surface of a first core (yoke) having slots for winding of a coil and a third core abutting against the top and bottom surfaces of the first core (yoke) so as to increase the effective area of the core and increase the saturation flux density and thereby enable a stronger magnetic field to be applied to the molten metal while retaining about the same outside shape as in conventional systems.
However, Japanese Patent No. 3273105 discloses a method of increasing the effective area of the core (yoke), but the specific ranges of numerical values of the space factor of the yoke sectional area (−) with respect to the inside area in the horizontal cross-section of the electromagnetic stirrer coil corresponding to that effective area and the yoke width B were not sufficiently studied, so a compact and high thrust electromagnetic stirrer coil could not be realized.